Transmission system for vehicle

ABSTRACT

An automatic transmission system for a vehicle having a plurality of drive gears mounted on an input shaft, a plurality of driven gears mounted on an output shaft and meshing with the drive gears, a torque converter disposed between a crankshaft of an engine and the input shaft, synchromesh mechanisms for synchronously engaging the drive gears with the driven gears and a shift controller for automatically actuating the synchromesh mechanisms so as to obtain a required gear ratio, includes a lock-up clutch incorporated in the torque converter for connecting a turbine shaft of the torque converter with the crankshaft, an electronically controlled throttle valve for automatically operating to reduce a rotation speed of the crank shaft when the gear is shifted, a bypass clutch for transmitting torque from the input shaft to the output shaft when the gear is shifted while the electronically controlled throttle valve operates to reduce a rotation speed of the crankshaft, an input clutch provided between an output element of the torque converter and the input shaft for selectively controlling a torque transmission from the crankshaft to the input shaft when the gear is shifted, and a brake mechanism provided on an impeller shell of the torque converter for additionally reducing a rotational speed of the crankshaft while the electronically controlled throttle valve operates to reduce a rotational speed of the crankshaft.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a transmission system for avehicle and more particularly to an automatic transmission whose geartrains are originated from those of a conventional manual transmission.

[0003] 2. Discussion of Prior Art

[0004] Generally, a manual transmission, in which the gear is manuallyshifted, has an input shaft directly connected to an engine and having aplurality of drive gears and has an output shaft having a plurality ofdriven gears paired with the drive gears and connected to drive wheels.That is, there are provided a plurality of shift gear trains between theinput shaft and the output shaft. When gear is changed, after a clutchis disengaged, changeover mechanisms such as synchromesh mechanism aremanually operated to change over paired shift gear trains and then theclutch is engaged. This sequence of manual operations accomplishes agear shift of a vehicle.

[0005] The manual transmission can be converted into an automatictransmission by replacing the sequence of those manual operations withautomatic operations using hydraulic actuators. This type of automatictransmission has advantages such as a small number of components, a goodtransmission efficiency of power and the like, compared to aconventional automatic transmission primarily constituted by planetarygears, friction engagement elements (clutches, brakes) and the like.

[0006] This type automatic transmission having a plurality of shift geartrains is called Automated Manual Transmission (hereinafter, referred toas “AMT”). Japanese Patent Application Laid-open No. Toku-Kai 2000-55184discloses an AMT including a main clutch (dry type clutch) for changingover the connection of a crank shaft with an input shaft between anengagement condition and a disengagement condition and a bypass clutch(hydraulically operated multiple disc clutch) for transmitting torquefrom the input shaft to an output shaft to prevent a so-called “torquedrop”. When the main clutch changes an engagement condition, the bypassclutch is engaged by hydraulic pressure so as to prevent an abrupt dropof output torque when the gear is shifted and thus a shift shock can bealleviated.

[0007] An AMT having a bypass clutch has an advantage that an abruptdrop of output torque can be prevented by the engagement of the bypassclutch at gearshifting. Time for switching over power through the bypassclutch at gearshifting is preferably as short as possible. Inparticular, when the gear is up-shifted during high speed revolution ofthe engine, it is necessary to synchronously engage a drive gear with adriven gear and reduce the engine speed as fast as possible and asaccurately as possible in order to smoothly change over gear trainsdoing power transmission by the changeover mechanism. That is, in orderto accomplish the shift operation swiftly, it is necessary to accuratelyreduce the revolution of the input shaft, or the engine speed up to asynchronous revolution speed. However, it is difficult to reduce theengine speed swiftly and accurately with the bypass clutch and theengine control using the electronic control throttle valve.

[0008] Hence, Japanese Patent Application Laid-open No. Toku-Kai-Hei4-203669 discloses a technology in which a brake is mounted on the inputshaft for the purpose of preventing an over-revolution of the enginewhen the gear is up-shifted and a synchronizer clutch is operated whenthe gear is down-shifted.

[0009] However, in this technology, since a clutch is released todisconnect power transmission from the engine to the input shaft atgearshifting, particularly, when the gear is shifted from the 1^(st)speed ratio to the 2^(nd) speed ratio or from the 2^(nd) speed ratio tothe 3^(rd) speed ratio, the change of driving force is so large that ashift shock can not be eliminated.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide an AMT typeautomatic transmission system having a bypass clutch capable of changinggears swiftly and smoothly.

[0011] To achieve the object, the automatic transmission system havingan input shaft, an output shaft, a plurality of drive gears mounted onthe input shaft, a plurality of driven gears mounted on the output shaftand meshing with the drive gears, a torque converter disposed between acrankshaft of an engine and the input shaft, synchromesh mechanisms forsynchronously engaging the drive gears with the driven gears and a shiftcontroller for automatically actuating the synchromesh mechanisms so asto obtain a required gear ratio, comprises a lock-up clutch incorporatedin the torque converter between the crankshaft and an output element ofthe torque converter for connecting the crankshaft with the input shaft,an electronically controlled throttle valve for automatically operatingto reduce a rotation speed of the crankshaft when the gear is shifted soas to smoothly synchronize the drive gears with the driven gears, abypass clutch for transmitting torque from the input shaft to the outputshaft when the gear is shifted, while the electronically controlledthrottle valve operates to reduce a rotation speed of the engine, aninput clutch disposed between the output element of the torque converterand the input shaft for selectively controlling a torque transmissionfrom the output element of the torque converter to the input shaft whenthe gear is shifted, and a brake mechanism disposed on an impeller shellof the torque converter for additionally reducing a rotational speed ofthe crankshaft while the electronically controlled throttle valveoperates to reduce a rotational speed of the crankshaft so as tosmoothly and swiftly engage the drive gears with the driven gears.

DESCRIPTION OF DRAWINGS

[0012]FIG. 1 is a skeleton diagram showing a transmission system for avehicle according to a first embodiment of the present invention;

[0013]FIG. 2 is an enlarged sectional view of FIG. 1;

[0014]FIG. 3 is a block diagram showing a control circuit of atransmission system for a vehicle according to the first embodiment ofthe present invention;

[0015]FIG. 4 is a timing chart showing a change of torque of an outputshaft versus engine speeds at an up-shift from the 1^(st) to 2^(nd) gearratio;

[0016]FIG. 5 is a skeleton diagram showing a transmission system for avehicle according to a second embodiment of the present invention;

[0017]FIG. 6 is a skeleton diagram showing a transmission system for avehicle according to a third embodiment of the present invention;

[0018]FIG. 7 is an enlarged sectional view of FIG. 6;

[0019]FIG. 8 is a skeleton diagram showing a transmission system for avehicle according to a fourth embodiment of the present invention;

[0020]FIG. 9 is a skeleton diagram showing a transmission system for avehicle according to a fifth embodiment of the present invention;

[0021]FIG. 10 is a skeleton diagram showing a transmission system for avehicle according to a sixth embodiment of the present invention;

[0022]FIG. 11 is an enlarged sectional view of FIG. 10;

[0023]FIG. 12 is a block diagram showing a control circuit of atransmission system for a vehicle according to the sixth embodiment ofthe present invention; and

[0024]FIG. 13 is a skeleton diagram showing a transmission system for avehicle according to a seventh embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0025] Referring now to FIG. 1, an engine 1 is provided with anelectronic control throttle valve 2 for electronically controllingengine torque and engine speeds. Normally, the electronic controlthrottle valve 2 is opened and closed by output signals from anelectronic control unit (not shown) according to the amount ofdepression of an accelerator pedal (not shown) to control the engine 1.Further, when needed, the electronic control throttle valve 2 can beopened and closed to control the engine 1 based on a preestablishedtable irrespective of the amount of depression of the accelerator pedal.

[0026] Further, a transmission system for transmitting power of theengine 1 to driving wheels is exemplified as a transmission system usedfor a four wheel drive vehicle in this embodiment. The transmissionsystem is mounted on a vehicle in a longitudinal direction thereof andhas an input shaft 3 connected to the engine 1 and an output shaft 4connected to driving wheels and disposed in parallel with the inputshaft. These input and output shafts are arranged in a longitudinaldirection of the vehicle in a transmission case 5. The input shaft 3 isconnected through a torque converter 6 to a crank shaft 7 of the engine1.

[0027] Drive gears 11, 12 for the 1^(st) gear ratio and the 2^(nd) gearratio respectively are fixed to the input shaft 3 and further drivegears 13, 14 and 15 for the 3^(rd), 4^(th) and 5^(th) gear ratiosrespectively are rotatably mounted on the input shaft 3. Further, drivengears 21, 22 for the 1^(st) and 2^(nd) gear ratios respectively arerotatably mounted on the output shaft 4 and driven gears 23, 24 and 25for the 3^(rd), 4^(th) and 5^(th) gear ratios respectively are fixed tothe output shaft 4. Respective drive gears 11 to 15 mesh with respectivedriven gears 21 to 25 to form respective shift gear trains. The gear isshifted by changing over the shift gear trains. Further, a drive gear 16for reverse speed is secured to the input shaft 1.

[0028] The output shaft 4 is provided with a first synchromesh mechanism31 between the driven gear 21 for the 1^(st) gear ratio and the drivengear 22 for the 2^(nd) gear ratio. The input shaft 3 is provided with asecond synchromesh mechanism 32 between the drive gear 33 for the 3^(rd)gear ratio and the drive gear 14 for the 4^(th) gear ratio and a thirdsynchromesh mechanism 33 adjacent to the drive gear 15 for the 5^(th)gear ratio.

[0029] The synchromesh mechanism 31 includes a synchronizer hub 31 asecured to the output shaft 2 and a synchronizer sleeve 31 b constantlymeshing with the synchronizer hub 31 a. When the synchronizer sleeve 31b meshes with a spline 21 a integrally formed with the driven gear 21for the 1^(st) gear ratio, the gear ratio is established to the 1^(st)gear ratio and when the synchronizer sleeve 31 b meshes with a spline 22a integrally formed with the driven gear 22 for the 2^(nd) gear ratio,the gear ratio is established to the 2^(nd) gear ratio.

[0030] Other synchromesh mechanisms 32, 33 include synchronizer hubs 32a, 33 a secured to the input shaft 1 and synchronizer sleeves 32 b, 33 bconstantly meshing with the synchronizer hubs 32 a, 33 a, respectively.When these synchronizer sleeves 32 b, 33 b are engaged with either ofthe corresponding splines 13 a, 14 a and 15 a, the gear ratio isestablished to either of the 3^(rd) to 5^(th) gear ratios.

[0031] The traveling in an axial direction and engagement with thesplines 21 a, 22 a, 13 a, 14 a and 15 a of the respective synchronizersleeves 31 b, 32 b and 33 b is performed by a hydraulic actuator (notshown).

[0032] The synchronizer sleeve 31 b of the first synchromesh mechanism31 is provided with a driven gear 26 for reverse speed. Further, anidler gear (not shown) is slidably mounted on an idler shaft (not shown)in parallel with the input and output shafts 3, 4 respectively so as toaxially travel between positions where the reverse driving gear 16 isengaged and disengaged with the driven gear 26. Accordingly, when theidler gear travels to mesh with the reverse drive gear 16 and thereverse driven gear 26 while the synchronizer sleeve 31b is a neutralposition, the output shaft 4 rotates in a reverse direction.

[0033] The output shaft 4 is hollowed around the center thereof and afront wheel output shaft 34 is incorporated in the hollow. The outputshaft 4 is connected with the front wheel output shaft 34 through acenter differential 35 and the front wheel output shaft 34 is connectedwith a front wheel drive shaft (not shown) through a front differential36. Further, the center differential 35 is connected with a rear wheeloutput shaft 39 through a drive gear 37 and a driven gear 38 and therear output shaft 39 is connected with a rear wheel drive shaft (notshown) through a rear differential (not shown).

[0034] A bypass gear 17 of the drive side is rotatably mounted on theinput shaft 3 and a bypass gear 27 of the driven side is secured to theoutput shaft 4. These gears 17, 27 are constantly in a meshingcondition. The input shaft 3 is provided with a bypass clutch 18 whichcomprises a clutch hub 20 fixed to the input shaft 3 and a clutch drum19 fixed to the bypass gear 17. The clutch drum 19 is provided with aplurality of clutch discs of the drive side and the clutch hub 20 isprovided with a plurality of clutch discs of the driven side. The clutchdiscs of the drive side are disposed in interleaving relation to theclutch discs of the driven side. Power of the input shaft 3 istransmitted to the output shaft 4 through the bypass clutch 18 bypressing those clutch discs by means of hydraulic pressure in an axialdirection. When releasing those clutch discs, power transmission isdisconnected between the input shaft 3 and the output shaft 4.

[0035] As shown in FIG. 2, the torque converter 6 has a pump side outershell 42 including a pump impeller 41 and a front cover 43 secured tothe outer shell 42. The front cover 43 is secured to a drive plate 44integrally connected with the crankshaft 7. A turbine runner 45 disposedopposite to the pump impeller 41 is directly connected with a turbineshaft 46 through a spline. The turbine shaft 46 is rotatablyincorporated in a hollow supporting shaft 47 and a stator 49 is providedon the supporting shaft 47 through an one-way clutch 48. The pump sideouter shell 42 and front cover 43 are an input element of the torqueconverter 6 respectively and the turbine runner 45 and turbine shaft: 46are an output element of the torque converter 6 respectively.

[0036] A lock-up clutch 51 is fitted over the turbine shaft 46 in such amanner that power can be transmitted when the lock-up clutch 51 ispressed on the front cover 43. There is provided an apply chamber 51 ato which hydraulic pressure is fed to press the loch-up clutch 51 on thefront cover 43 on one side of the lock-up clutch 51 and there isprovided a release chamber 51 b from which hydraulic pressure isreleased to disengage the lock-up clutch 51 on the other side thereof.When hydraulic pressure is fed to the release chamber 51 b and iscirculated through the apply chamber 51 a, the lock-up clutch 51 isreleased and the torque converter 6 is operative. On the other hand,when hydraulic pressure is fed to the apply chamber 51 a and hydraulicpressure in the release chamber 51 b is reduced, a clutch disc 52 of thelock-up clutch 51 is pressed by the front cover 43 to produce a lock-upcondition. The lock-up clutch 51 is engaged when vehicle speed exceeds aspecified value based on a table parameterizing vehicle speeds andaccelerator pedal opening angles. Thus, power of the crankshaft 7 istransmitted to the turbine shaft 46 through the torque converter 6 orthe lock-up clutch 51.

[0037] There is provided an input clutch 53 between the turbine shaft 46and the input shaft 3. The input clutch 53 comprises a clutch drum 54fixed to the turbine shaft 46 and a clutch hub 55 secured to the inputshaft 3 through a spline. When a clutch drive disc 54 a mounted on theclutch drum 54 is engaged with a clutch driven disc 55 a mounted on theclutch hub 55, the turbine shaft 46 is connected with the input shaft 3.When the engagement is released, the turbine shaft 46 is disconnectedfrom the input shaft 3.

[0038] As shown in FIG. 2, a clutch piston 56 is mounted in the clutchdrum 54. When hydraulic pressure is supplied to an oil chamber 56 a, theclutch drive disc 54 a is engaged with the clutch driven disc 55 a andwhen hydraulic pressure is stopped to be supplied, the engagement isreleased by the spring force of spring member 57.

[0039] An oil pump 59 is incorporated in a supporting wall 58 connectedwith the transmission case 5. A rotor of the oil pump 59 is driveablyconnected with an extension member of the pump side outer shell 42 ofthe torque converter 6 and is driven by the crankshaft 7 through thepump side outer shell 42. Hydraulic fluid discharged from the oil pump59 is supplied to the torque converter 6, the bypass clutch 18, theinput clutch 53, hydraulically operated devices such as the aforesaidhydraulic actuators and lubricating parts after being converted into ahydraulic fluid with a specified hydraulic pressure for each device.

[0040] There is provided a brake mechanism 61 outside of the outer shell42 on the pump side. The brake mechanism 61 has a brake disc 82 securedto the outer shell 42 and a caliper 63 for braking the brake disc 62 byclamping the disc in between. The caliper 63 is mounted on thetransmission case 5.

[0041] As shown in FIG. 2, the caliper 63 is mounted on a caliper body64 secured to the transmission case 5. The caliper body 64 includes twohydraulic cylinders 65 a and 65 b which are provided opposite to eachother. The respective hydraulic cylinders 65 a, 65 b have hydraulicpistons 66 a, 66 b on which brake pads 67 a, 67 b are installedrespectively so as to interleave the brake disc 62.

[0042] Accordingly, when working fluid is supplied to the respectivehydraulic cylinders 65 a, 65 b in accordance with vehicle operatingconditions, the brake disc 62 contacts the brake pads 67 a, 67 b toreduce the rotation speed of the crankshaft 7. For example, when thebrake mechanism 61 is operated at an up-shift, since the electroniccontrol throttle valve 2 additionally reduces the engine speed, therotation speed of the crankshaft 7 descends to a specified value for avery short time. As a result, the shift operation can be performedsmoothly and swiftly. Further, since a braking force is applied to thecrankshaft 7 at a radially remote place on the outer shell 42 of thetorque converter 6, a large braking force can be obtained withoutapplying a large pressing force on the brake pads 67 a, 67 b.

[0043] Referring to FIG. 3, a shift controller 70 inputs a rotationalspeed of the crankshaft 7 from an engine speed sensor 71, a throttlevalve opening angle from a throttle valve opening angle sensor 72, atraveling speed of a vehicle from a vehicle speed sensor 73, a range ofthe automatic transmission like drive range, neutral range from aninhibitor switch 74 and a brake signal indicative of an abrupt brakingfrom a brake sensor 75 by detecting a depression amount of a brakepedal.

[0044] The bypass clutch 18, the lock-up clutch 51 and the input clutch53 are actuated by means of hydraulic pressure regulated byelectromagnetic valves provided in a valve control unit 76. The valvecontrol unit 76 is controlled by signals from the shift controller 70.Further, the synchronizer sleeves 31 b, 32 b and 33 b are actuated forengagement in the axial direction by a plurality of hydraulic actuators77. Regulated hydraulic pressure is supplied to the respective actuators77 from the electromagnetic valves provided in the valve control unit76. The shift controller has a memory in which a shift tableparameterizing throttle opening angles, vehicle speeds and the like isstored so as to automatically perform a shift operation by detectingactual engine speeds, accelerator pedal opening angles, vehicle speeds,rotation speed of the output shaft, gear positions and the like.

[0045] When a selector lever provided in the passenger compartment ispositioned at a neutral range under an engine operative condition, bothlock-up clutch 71 and input clutch 73 are established in a releasedcondition.

[0046] When the selector lever selects a forward drive range, since theselector lever is interlocked with one of manual valves (not shown) of ahydraulic control mechanism incorporated in the transmission system, theinput clutch 53 is engaged by hydraulic pressure supplied thereto. Atthis moment, there is a sequence to operate the input clutch 53. First,an hydraulic actuator slides the synchronizer sleeve 31 b and engages itwith the spline 21 a to place this shift gear train for the 1^(st) gearratio in a power transmitting condition. After that, hydraulic pressureis supplied so as to engage the input clutch 53. Thus, engine power istransmitted to the input shaft 3 through the torque converter 6 and theinput clutch 53 to drive the vehicle. Then, engine torque transmitted tothe input shaft 3 is amplified by the torque converter 6.

[0047] As the accelerator pedal opening angle increases, the electroniccontrol throttle valve 2 operates and up-shifts are performed. When thevehicle speed goes down or when the accelerator pedal is suddenlydepressed (kick down), down-shifts are performed. The gear is shiftedautomatically according to shift schedules programmed in a shift controlsection.

[0048] At up-shifting, while the input clutch 53 is retained in such acondition as being able to variably transmit torque according to vehicleoperating conditions, the bypass clutch 18 starts to be engaged and thenis controlled so as to gradually increase the transmission torque of thebypass clutch 18. For example, the engine speed is reduced to aspecified value corresponding to the 2^(nd) gear ratio by controllingthe electronic control valve 2 to synchronize and engage thesynchronizer sleeve 31 b with the spline 22 a of the driven gear 22 of2^(nd) gear ratio. At this moment, when the gear is changed, power istransmitted from the input shaft 3 to the output shaft 4 through thebypass gears 17 and 27 due to the engagement of the bypass clutch 18without shutting off power of the engine and as a result torque dropscan be eliminated at gearshifting.

[0049] The input shaft 3 can be synchronously engaged with the outputshaft 4 through the bypass clutch 18, while a torque drop between theinput shaft 3 and the output shaft 4 is prevented. Further, when thegear is up-shifted, since the rotation speed of the input shaft 3 can bereduced in short time with accuracy to a specified number of revolutionby simultaneously operating both the brake mechanism 61 and theelectronic control throttle valve 2, fast synchronous engagements areobtained when the gear trains steps from a low speed stage to a highspeed stage. On the other hand, when the gear is down-shifted, since theengine speed can be raised by the control of the electronic controlthrottle valve 2, the input shaft 3 can be synchronously and smoothlyengaged with the output shaft 4.

[0050] When the vehicle starts, the input clutch 53 is in an engagedcondition. Further, when the vehicle travels, the input clutch 53 isalso in an engaged condition. When the gear is down-shifted, if theinput clutch 53 stays in an engaged condition, drag torque retainsengine speed in a reduced condition. Hence, at down-shifting, the inputclutch 53 is controlled so as to be partially engaged, that is, in aslip condition and as a result it becomes possible to increase theengine speed at down-shifting.

[0051] For example, when the vehicle travels at low or medium speedunder a high speed stage such as the 4^(th) or 5^(th) speeds, the ridingcomfort is exacerbated due to the effect of torque fluctuation at lowengine speeds. Under these traveling conditions, when the input clutch53 is engaged in a minimum torque transmission condition, the inputclutch 53 acts as a dumper and the torque fluctuation is prevented frombeing transmitted to a vehicle drive train. As a result, the ridingcomfort is prevented from being exacerbated.

[0052] Since the lock-up clutch 51 is incorporated in the torqueconverter 6, in order to supply hydraulic pressure from anelectromagnetic valve provided in the valve control unit 76 to thelock-up clutch 51, a long oil delivery path is required. Further, sincethe lock-up clutch 51 is operated by a pressure difference between theapply chamber 51 a and the release chamber 51 b, in case where oiltemperature is low, it takes a long time for the lock-up clutch 51 tochange over from an engaged condition to a released condition due to theeffect of viscosity of working fluid. As a result, when the engine speedgoes down while the engine is connected with the input shaft 3, enginestalls may occur.

[0053] On the other hand, the input clutch 53 is designed such that whenhydraulic pressure is supplied to the oil chamber 56 a, the input clutch53 is engaged and when oil is discharged from the oil chamber 56 a, theinput clutch 53 is released. Furthermore, since the input clutch 53 isdisposed in a place close to an electromagnetic valve provided in thevalve control unit 76, the oil delivery path from the electromagneticvalve to the input clutch 53 is shorter than that from theelectromagnetic valve to the lock-up clutch 51 and as a result the inputclutch 53 has a better responsibility than the lock-up clutch 51.Therefore, when abrupt braking is applied, the input clutch 53 isreleased while the lock-up clutch 51 is engaged. As a result, when theengine speed goes down abruptly, engine stalls can be prevented.

[0054]FIG. 4 is a timing chart showing a time-versus change of a torqueTo of the output shaft 4 and a time-versus change of an engine speed Newhen the gear is up-shifted from the 1^(st) to 2^(nd) gear ratio.

[0055] In the drawing, a shift position indicates a position of thesynchronizer sleeve 31 b. That is, the state “1^(st) speed” indicatesthat the synchronizer sleeve 31 b is engaged with the driven gear 21through the spline 21 a, the state “Neutral” indicates that thesynchronizer sleeve 31 b is disengaged from the spline 21 a, and thestate “2^(nd) speed” indicates that the synchronizer sleeve 31 b isengaged with the driven gear 22 through the spline 22 a.

[0056] In a power delivery path “1^(st) gear train”, engine power istransmitted to the output shaft only through the 1^(st) speed gear trainand in a power delivery path “Phase I”, engine power is transmitted tothe output shaft through both the 1^(st) speed gear train and the bypassclutch 18. In a power delivery path “Phase II”, engine power istransmitted only through the bypass clutch 18. Further, in a powerdelivery path “Phase III”, power is transmitted through both the 2^(nd)speed gear train and the bypass clutch 18 and in a power delivery path“2^(nd) gear train”, engine power is transmitted only through the 2^(nd)speed gear train.

[0057] When a gear shift is performed, first, hydraulic pressure issupplied to the bypass clutch 18, a condition where power is transmittedthrough the 1^(st) speed gear train formed by the drive gear 11 and thedriven gear 21 changes to a condition of Phase I where power istransmitted through two power delivery paths, the 1^(st) speed geartrain and the gear train of the bypass gears 17 and 27.

[0058] Since the drive gear 11 of the 1^(st) gear ratio driveably mesheswith the driven gear 21 and on the other hand the bypass gear 17 drivesthe bypass gear 27, the bypass gear 17 rotates at a higher speed thanthe drive gear 11 due to the difference of gear ratios. As a result,torque is transmitted through the gear train of the bypass gears 17, 27according to the engagement condition of the bypass clutch 18.

[0059] Next, the synchronizer sleeve 31 b transfers to a neutralposition, namely the Phase II condition, in which the synchronizersleeve 31 b meshes only with the synchronizer hub 31 a. Under thecondition, power is transmitted from the input shaft 3 to the outputshaft 4 through the gear train of the bypass gears 17, 27 and at thesame time the rotational speed of the input shaft 3 is reduced by theclosing operation of the electronic control throttle valve 2 tosynchronize the input shaft 3 with the output shaft 4. At this moment,the brake mechanism 61 operates to brake the crankshaft 7 and as aresult time for synchronizing can be shortened.

[0060] When the engine rotational speed is reduced to a levelcorresponding to the 2^(nd) speed, a condition where the synchronizersleeve 31 b meshes only with the synchronizer hub 31 a transfers to acondition where the synchronizer sleeve 31 b meshes with the spline 22a. As a result, in this condition, Phase III condition, the powerdelivery path has two paths, one is a shift gear train of the 2^(nd)speed and another is a gear train of the bypass gears 17, 27. When thesynchronizer sleeve 31 b comes into a meshing condition with the spline22 a, the braking torque of the brake mechanism 61 is released and nobraking force is applied to the crankshaft 7.

[0061] Under the Phase III condition, when hydraulic pressure fed to thebypass clutch 18 is drained to release the bypass clutch 18, an up-shiftto the 2^(nd) speed is accomplished and then power is transmitted fromthe input shaft 3 to the output shaft 4 through the gear train of the2^(nd) speed.

[0062] Thus, the bypass clutch control and the engine control areperformed simultaneously and when the rotational speed of the engine isreduced to a speed corresponding to the 2^(nd) speed, the synchronizersleeve 31 b meshes with the spline 22 a. As a result, no gear clashoccurs and the shift operation can be accomplished smoothly. Further,when the synchronizer sleeve 31 b is at a neutral position, since poweris transmitted through the bypass clutch 18, so-called “torque drop” canbe reduced. Particularly, the torque drop becomes noticeable when thegear is up-shifted from the 1^(st) speed to the 2^(nd) speed or from the2^(nd) speed to the 3^(rd) speed.

[0063] Referring to FIG. 4, two-dots chain lines indicate a change ofengine speeds when the brake mechanism 61 is inoperative and solid linesindicate a change of engine speeds when the brake mechanism 61 isoperative. As understood from the difference of these changes, when thebrake mechanism 61 is operative, since time for transmitting power fromthe input shaft 3 to the output shaft 4 only through the bypass clutch18, that is, time in the Phase II condition can be shortened surely andaccurately, the total time for gearshifting can be shortened.

[0064]FIG. 4 shows a change of engine speeds and torque when the gear isup-shifted from the 1^(st) to 2^(nd) gear ratio. Other up-shiftoperations such as an operation from the 2^(nd) to 3^(rd) gear ratiosand the like are done in a similar manner. As understood from FIG. 4, agearshift operation at up-shifting can be done swiftly. In case wherethe gear ratio of the bypass gears 17, 27 of the bypass clutch 18 isselected to a value corresponding to that of the 4^(th) speed, when thegear is up-shifted to high speed stages such as from the 4^(th) speed tothe 5^(th) speed, the gear may be shifted without involving the bypassclutch 18 (with the bypass clutch 18 released), because the gear ratioof the bypass gears is near to that of the 4^(th) speed and accordinglythe drop of driving force is small.

[0065] On the other hand, when the gear is down-shifted, since the dropof output torque is not so noticeable, the input clutch 53 may beoperated to shut off power transmission to the input shaft 3. Further,also when the gear is down-shifted, the bypass clutch 18 may be engagedso as to change over the control between power deliveries through twopaths and power transmission only through the bypass clutch 18 while theengine control and the brake control by the brake mechanism 61 areperformed.

[0066]FIG. 5 is a skeleton diagram showing a transmission systemaccording to a second embodiment of the present invention. Thecomponents identical to the first embodiment are denoted by identicalreference numbers and are not described in detail.

[0067] In this transmission system, the brake mechanism 61 is providedon an outer side of the clutch drum 54 of the input clutch 53. Aplurality of spline grooves 81 having grooves in an axial direction arecircumferentially formed integrally with the transmission case 5 and aplurality of driven discs 81 a are fitted to the spline grooves 81.Further, a plurality of drive discs 54 b are driveably mounted on splineteeth formed on the outer side of the clutch drum 54. The drive discs 54b contact the driven discs 81 a in an interleaving manner with eachother. When hydraulic pressure is applied to these drive discs 54 b andthe driven discs 81 a, an engagement force generates between thesediscs. Brake torque of the brake mechanism 61 is regulated by adjustingthe engagement force with hydraulic pressure. As shown in FIG. 5, sincecomponents of the brake mechanism 61 is coaxially formed on an outerperiphery of the clutch drum 54 of the input clutch 53, the axial lengthof the transmission system can be shortened. In order to smoothlycontrol the rotation of the crankshaft 7 of the transmission system, thebrake mechanism 61 is operated while the lock-up clutch 51 which isdirectly connected with the crankshaft 7 is engaged. Thus, since theinput clutch 53 is driveably connected with the crankshaft 7, enginepower can be directly transmitted to the input shaft 3 by engaging theinput clutch 53. As a result, the gear can be shifted smoothly and fueleconomy in medium to high speed ranges can be enhanced due to very smallloss of power transmission.

[0068] In case of the transmission system of a third embodiment shown inFIG. 6 and FIG. 7, the brake mechanism 61 is disposed between the stator49 of the torque converter 6 and the supporting shaft 47 for supportinga reaction torque of the stator 49. The brake mechanism 61 includes abrake drum 82 secured to the supporting shaft 47 through spline fittingand a brake hub 83 fixed to the pump side outer shell 42. Brake drivendiscs 82 a are mounted on the brake drum 82 and brake drive discs 83 aare driveably mounted on the brake hub 83. Further, the brake drivendiscs 82 a have contact with the brake drive discs 83 a.

[0069] A brake piston 84 is slidably incorporated in the brake drum 82.When working fluid is fed to an oil chamber 84 a, the brake discs 82 aand 83 a generate an engagement force. Braking torque of the brakemechanism 61 is regulated by adjusting the engagement force of the brakediscs 82 a, 83 a. The brake piston 84 is subjected to a biasing force ina releasing direction by a spring member 85.

[0070] In this transmission system, since the brake mechanism 61 isdisposed inside of the stator 49 of the torque converter 6, the axial orlongitudinal size of the transmission system can be shortened. As aresult, the transmission system can be introduced into a variety oftypes of transmission.

[0071]FIG. 8 is a skeleton diagram showing a transmission systemaccording to a fourth embodiment. In this transmission system, the brakemechanism 61 is formed between the pump side outer shell 42 of thetorque converter 6 and the transmission case in the same manner as inthe first embodiment. On the other hand, the lock-up clutch 51 isdriveably connected with the input shaft 3. When the lock-up clutch 51is engaged, the crankshaft 7 is directly connected with the input shaft3. The input clutch 53 is incorporated between the turbine runner 45 ofan output element of the torque converter 6 and the lock-up clutch 51.

[0072] The input clutch 53 comprises a clutch drum 54 fixed to theturbine runner 45, a clutch drive disc 54 a mounted on the clutch drum54, a clutch hub 55 which is connected to the input shaft 3 and a clutchdriven disc 55 a mounted on the clutch hub 55. The rotation of theturbine runner 45 is transmitted to the input shaft 3 through the inputclutch 53. Accordingly, in case where the input clutch 53 is disengagedand the lock-up clutch 51 is engaged, or in case where the input clutch53 is engaged and the lock-up clutch 51 is released, the rotation of thecrankshaft 7 is directly transferred to the input shaft 3.

[0073]FIG. 9 is a skeleton diagram showing a fifth embodiment of atransmission system.

[0074] In this transmission system, the input clutch 53 is disposedbetween an output element of the turbine runner 45 and an input elementof the lock-up clutch 51 in the same manner as in case of FIG. 8 and thebrake mechanism 61 is provided on an inner periphery surface of thestator 49 of the torque converter 6.

[0075] In these transmission systems shown in FIG. 8 and FIG. 9, sincethe input clutch 53 and the lock-up clutch 51 are integrallyincorporated in the torque converter 6 and the clutch drum of the inputclutch 53 is driveably connected with the turbine runner 45, the axialor length of the transmission system can be shortened. As a result, avariety of transmission types, transversely mounted type, longitudinallymounted type and the like, can introduce these transmission systems.

[0076] The transmission systems described before in the second, third,fourth and fifth embodiments have automatic transmissions comprising thetorque converter 6, the input clutch 53, the brake mechanism 61, aplurality of shift gear trains and the bypass clutch 18 for transmittingtorque from the input shaft 3 to the output shaft 4 when needed. Thesetransmission systems perform similar shift operations to thetransmission system described in the first embodiment.

[0077]FIG. 10 shows a transmission system according to a sixthembodiment. The transmission system comprises a flywheel dumper 90, aninput clutch 53, a brake mechanism 61, a plurality of shift gear trainsand a bypass clutch 18, not including a torque converter.

[0078] As shown in FIG. 10 and FIG. 11, the flywheel dumper 90 comprisesa drive plate 91 driveably secured to the crankshaft 7 and a drivenplate 93 connected with the drive plate through a spring member 92 forabsorbing shocks. The driven plate is spline-fitted over a rotationshaft 94 which is rotatably supported by the supporting wall 58 of thetransmission case 5.

[0079] The input clutch 53 includes the clutch drum 54 secured to therotation shaft 94 and the clutch hub 55 secured to the input shaft 3.Similarly to the first embodiment, there are provided clutch drive discs54 a and clutch driven discs 55 a interleaving relationship with eachother between the clutch drum 54 and the clutch hub 55. When hydraulicpressure is supplied to the oil chamber 56 a, the clutch piston 56presses the clutch discs 54 a, 55 a and as a result an engagement forcegenerates between the clutch discs 54 a, 55 a, thus the input clutch 53being engaged. Further, according to the magnitude of hydraulic pressureapplied to the oil chamber 56 a, the input clutch 53 can retained in anyconditions from a partially engaged or slip condition to a fully engagedcondition. When hydraulic pressure is stopped to be supplied to the oilchamber 56 a, the engagement force is lost by the spring member 57, theinput clutch 53 being released.

[0080] With respect to the brake mechanism, the brake disc 62 is fixedto an extension member of the drive plate 91. Accordongly, the brakedisc 62 is directly connected with the crankshaft 7. Except this, theconstruction of the brake mechanism 61 is similar to those of the firstand fourth embodiments.

[0081]FIG. 12 is a block diagram showing a shift control of atransmission system according to the sixth embodiment of the presentinvention. Except that the lock-up clutch 51 is deleted, othercomponents such as the input clutch 53, the bypass clutch 18, the brakemechanism 61 and the hydraulic actuators 77, operate in the same manneras in the aforesaid embodiments.

[0082] According to this transmission system, since the brake mechanism61 is accommodated outside of the outer periphery of the clutch drum 54of the input clutch 53 and provided on the extension member of theflywheel dumper 90, the axial size of the transmission can be reducedand the requirement of braking torque can be obtained with compactconstruction.

[0083]FIG. 13 is a skeleton diagram showing a transmission systemaccording to a seventh embodiment. The transmission system comprises theflywheel dumper 90, an input clutch 53, a brake mechanism 61, aplurality of shift gear trains and a bypass clutch 18 in the same manneras the sixth embodiment. The difference between this embodiment and thesixth embodiment is that the brake system of the sixth embodiment is adisc brake type and on the other hand the brake system of the seventhembodiment is a multiple disc brake type of which construction is thesame as that of the second embodiment.

[0084] According to this transmission system, since the brake mechanism61 is provided around the clutch drum 54 of the input clutch 53, anup-sizing of the transmission in an axial direction in incorporating thebrake mechanism 61 into the transmission can be prevented.

[0085] While the present invention has been disclosed in terms of thepreferred embodiments in order to facilitate better understanding of theinvention, it should be appreciated that the invention can be embodiedin various ways without departing from the principle of the invention.Therefore, the invention should be understood to include all possibleembodiments which can be embodied without departing from the principleof the invention set out in the appended claims.

What is claimed is:
 1. An automatic transmission system for a vehiclehaving an input shaft, an output shaft, a plurality of drive gearsmounted on said input shaft, a plurality of driven gears mounted on saidoutput shaft and meshing with said drive gears, a torque converterdisposed between a crankshaft of an engine and said input shaft,synchromesh mechanisms for synchronously engaging said drive gears withsaid driven gears and a shift controller for automatically actuatingsaid synchromesh mechanisms so as to obtain a required gear ratio,comprising: a lock-up clutch incorporated in said torque converterbetween said crankshaft and an output element of said torque converterfor connecting said crankshaft with said input shaft; an electronicallycontrolled throttle valve for automatically operating to reduce arotation speed of said crankshaft when the gear is shifted so as tosmoothly synchronize said drive gears with said driven gears; a bypassclutch for transmitting torque from said input shaft to said outputshaft when the gear is shifted, while said electronically controlledthrottle valve operates to reduce a rotation speed of said engine; aninput clutch disposed between said output element of said torqueconverter and said input shaft for selectively controlling a torquetransmission from said output element of said torque converter to saidinput shaft when the gear is shifted; and a brake mechanism foradditionally reducing a rotational speed of said crankshaft while saidelectronically controlled throttle valve operates to reduce a rotationalspeed of said crankshaft so as to smoothly and swiftly engage said drivegears with said driven gears.
 2. The automatic transmission systemaccording to claim 1, wherein said brake mechanism is disposed on animpeller shell of said torque converter between said impeller shell anda transmission case.
 3. The automatic transmission system according toclaim 1, wherein said brake mechanism is mounted on an a clutch drum ofsaid input clutch between said clutch drum and a transmission case. 4.The automatic transmission system according to claim 1, wherein saidbrake mechanism is incorporated in said torque converter between amember constituting said impeller shell of said torque converter and afixed member for supporting a reaction torque of a stator.
 5. Theautomatic transmission system according to claim 1, wherein said inputclutch is incorporated in said torque converter integrally with saidlock-up clutch.
 6. An automatic transmission system for a vehicle havingan input shaft, an output shaft, a plurality of drive gears mounted onsaid input shaft, a plurality of driven gears mounted on said outputshaft and meshing with said drive gears, a flywheel disposed between acrankshaft of an engine and said input shaft, synchromesh mechanisms forsynchronously engaging said drive gears with said driven gears and ashift controller for automatically actuating said synchromesh mechanismsso as to obtain a required gear ratio, comprising: an electronicallycontrolled throttle valve for automatically operating to reduce arotation speed of said crankshaft when the gear is shifted so as tosmoothly synchronize said drive gears with said driven gears; a bypassclutch for transmitting torque from said input shaft to said outputshaft when the gear is shifted, while said electronically controlledthrottle valve operates to reduce a rotation speed of said engine; aninput clutch is disposed between said flywheel and said input clutch forselectively controlling a torque transmission from said output elementof said torque converter to said input shaft when the gear is shifted;and a brake mechanism for additionally reducing a rotational speed ofsaid crankshaft while said electronically controlled throttle valveoperates to reduce a rotational speed of said crankshaft so as tosmoothly and swiftly engage said drive gears with said driven gears. 7.The automatic transmission system according to claim 6, wherein saidbrake mechanism is mounted on said flywheel between said flywheel and atransmission case.
 8. The automatic transmission system according toclaim 6, wherein said brake mechanism is mounted on a clutch drum ofsaid input clutch between said clutch drum and a transmission case. 9.An automatic transmission system for a vehicle having an input shaft, anoutput shaft, a shift gear train provided between said input shaft andsaid output shaft, a coupling device connecting a crankshaft of anengine and said input shaft and a controller for connecting a gearshifting of said gear shift train to obtain a required gear ratio,comprising: an input clutch provided to control a torque transmission tosaid shift gear train during said gear shifting; a bypass clutchprovided to control a torque transmission from said input shaft to saidoutput shaft during said gear shifting; an electronically controlledthrottle valve of said engine operative to reduce a rotation speed ofsaid crankshaft during gear shifting, and a brake mechanism provided toreduce a rotational speed of said crankshaft in cooperation with saidelectronically controlled throttle valve during said gear shifting.